Preparation method of high-surface-quality titanium alloy investment precision casting shell

Abstract

The invention provides a preparation method of a high-surface-quality titanium alloy precision investment casting shell, and relates to the technical field of precision investment casting, and the preparation method comprises the following steps: S1, wax mold cleaning; the wax mold is sequentially cleaned through the cleaning agent solution and the cleaning solution, and the step is repeated for 1-3 times; s2, preparing surface layer slurry; s3, preparing a surface layer; and S4, preparing a back layer. In the step S1, the cleaning agent solution is prepared from the following components in percentage by mass: 0.1 to 0.3 percent of detergent, 0.03 to 0.15 percent of JFC wetting agent and 0.3 to 0.15 percent of clear water. According to the wax mold cleaning and drying method, the coating property of the surface layer slurry is improved, and the quality of the wax mold and a surface mold shell is improved; according to the surface layer slurry, the surface layer bonding strength can be improved, the unshelling performance is improved, and the surface roughness of a casting is reduced; according to the vacuum slurry dipping technology, the surface layer slurry is effectively promoted to fill the fine shape of the wax mold, the defects of slits, narrow grooves, corners, blind holes and the like are eliminated, and the defects of casting knots, slag inclusion and the like of subsequent pouring castings are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of investment precision casting, and more specifically, to a method for preparing an investment precision casting shell for titanium alloy with high surface quality. Background Art

[0002] Titanium alloy has excellent properties such as low density and high specific strength. Various complex structure castings formed by the investment casting process are widely used in the fields of aviation, aerospace, navigation, chemical industry, petroleum, medicine, etc. Investment casting can meet the requirements of dimensional accuracy while satisfying good formability of castings, and is suitable for batch production of near-net-shape castings with complex structures. The quality of the shell has a significant impact on the surface quality of the casting. The process for preparing an investment casting shell for titanium alloy is to coat several layers of special refractory coatings on the surface of a fusible pattern, and then form an integral shell after drying. The fusible pattern is removed with hot steam to obtain a cavity. When the casting has a semi-closed structure with narrow slits or grooves, the slurry of the conventional surface layer shell-making process accumulates in the gaps during coating, and sand grains form bridges, which are likely to cause casting defects such as casting tumors and slag inclusions during pouring. For near-net-shape precision parts, eliminating such defects will lead to problems such as excessive grinding and dimensional deviation, and easily cause batch quality problems of castings.

[0003] CN102284678A discloses a method for preparing a precision casting titanium alloy mold shell, and the steps are as follows: 1) Prepare the surface layer; 2) Prepare the transition layer; 3) Prepare the reinforcement layer; 4) Dewax and sinter. In the prior art, the wax pattern is not treated, the coating property of the surface layer slurry is poor, the surface quality of the prepared mold shell is poor, and the bonding strength of the surface layer slurry is low and the shell removal performance is weak, resulting in a relatively large surface roughness of the casting. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method for preparing an investment precision casting shell for titanium alloy with high surface quality, so as to solve the problems in the prior art that the wax pattern is not treated, the coating property of the surface layer slurry is poor, the surface quality of the prepared mold shell is poor, and the bonding strength of the surface layer slurry is low and the shell removal performance is weak, resulting in a relatively large surface roughness of the casting.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A method for preparing an investment precision casting shell for titanium alloy with high surface quality includes the following steps:

[0007] S1. Wax pattern cleaning: The wax pattern is successively cleaned with a cleaning agent solution and a cleaning solution, and steps 1 to 3 are repeated 1 to 3 times;

[0008] S2. Preparation of surface layer slurry;

[0009] S3. Preparation of surface layer;

[0010] S4. Preparation of the back layer.

[0011] In the preparation of the shell mold, by repeatedly cleaning the wax pattern with a cleaning agent solution and a cleaning solution, the coating property of the surface layer slurry is increased, and the quality of the wax pattern and the surface shell mold is improved.

[0012] Further, in step S1, the cleaning agent solution includes dishwashing liquid, JFC wetting agent, and clear water. Among them, the mass fraction of the dishwashing liquid is 0.1% - 0.3%, and the mass fraction of the JFC wetting agent is 0.03% - 0.15%.

[0013] Further, in step S1, the cleaning solution is JFC wetting agent and clear water. Among them, the mass fraction of the JFC wetting agent is 0.03 - 0.15%.

[0014] Further, in step S2, the surface layer slurry uses modified silica sol. The modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator. The mass ratio of the diluted silica sol to the PVA solution is 15 - 25:1. The mass fraction of PVA in the PVA solution is 10% - 20%. The acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9 - 10.

[0015] This setting can ensure the strength of the surface layer, and at the same time, can reduce the high-temperature interface reaction, reduce the pores and pits on the surface of the casting, and improve the shell stripping performance.

[0016] Further, the mass fraction of SiO2 in the diluted silica sol is 15% - 20%.

[0017] Further, in step S2, the specific steps are as follows: Add yttrium oxide powder to the modified silica sol, where the powder-liquid mass ratio is 3.5 - 5.5:1, and then add JFC wetting agent and disperse evenly to prepare a surface layer slurry with a flow cup viscosity of 6 - 12 s.

[0018] The composition of the surface layer slurry in this setting can increase the bonding strength of the surface layer, improve the shell stripping performance, and reduce the surface roughness of the casting.

[0019] Further, the mesh number of the yttrium oxide powder is 200 - 400 mesh, preferably 325 mesh.

[0020] Further, the mass ratio of the JFC wetting agent to the total mass of the modified silica sol and yttrium oxide powder is 0.03% - 0.15%.

[0021] Further, in step S2, mechanical stirring is used for uniform dispersion, and the rotation speed is 180 - 250 r / min.

[0022] Further, the specific preparation steps of the diluted silica sol are as follows: Using ordinary silica sol, deionized water as the solvent, diluting the silica content to 15% - 20%, adding a pH regulator to adjust the pH value to 9 - 10, and stirring for about 24 - 48 hours. Here, the pH regulator is NaOH solution and HCl solution.

[0023] This setting can reduce the high-temperature interface reaction, reduce the pores and pitting defects on the surface of the casting, and improve the shell stripping performance.

[0024] Further, the specific preparation steps of step S3 are as follows: Place the wax pattern in a container, pour the surface layer slurry of step S2 into the container, and submerge the wax pattern to a certain height, with the height being sufficient to cover the wax pattern. Place the entire container into a vacuum equipment, perform the sealing work well, set a certain vacuum degree and start the vacuum equipment. After the wax pattern stops bubbling, end the vacuum treatment, manually release the negative pressure, and the liquid level of the surface layer slurry drops, completing the vacuum dipping of the wax pattern; then apply the surface layer to other parts of the wax pattern that are not dipped. The application can adopt the traditional application method. Then, sand is scattered by the rain-type sand scattering method. The surface layer sand used is one of yttrium oxide sand, zirconium oxide sand, and composite aluminum zirconium sand, with a mesh number of 60 - 120 meshes. The surface layer drying is carried out in a constant temperature and humidity workshop, with a drying time of 8 - 12 hours, a temperature of 21 - 25 °C, and a humidity not less than 75%. For the shell with complex and fine structures such as narrow slots, micropores, or high surface accuracy requirements, the surface layer vacuum dipping can be repeated 1 - 2 times after drying.

[0025] This setting effectively promotes the filling of the surface layer slurry into the fine shapes of the wax pattern, eliminates the defects of air entrapment and air / bean bubbles in the slurry at narrow slots, corners, blind holes, etc., and avoids the subsequent defects such as casting tumors and slag inclusions in the castings during pouring.

[0026] Further, in step S4, when preparing the back layer, back layer slurry and back layer sand are used. The back layer slurry includes back layer silica sol and mullite powder. The back layer silica sol is silica sol with a SiO2 content of 30%, and the mullite powder uses 200 - mesh mullite powder. The back layer sand uses 16 - 60 - mesh mullite sand.

[0027] Further, in step S4, the back layer includes back layer 1, back layer 2, back layer 3, back multiple layers, and back multiple layers means more than three layers;

[0028] Back layer 1 includes back layer 1 slurry and back layer 1 sand. The back layer 1 slurry is prepared with mullite powder and back layer silica sol according to a powder - liquid mass ratio of 1.0 - 1.5:1. The back layer 1 sand uses manually scattered 30 - 60 - mesh mullite sand and is dried in a constant temperature and humidity workshop for 12 - 24 hours;

[0029] The back layer 2 includes back layer 2 slurry and back layer 2 sand. The back layer 2 slurry is prepared from mullite powder and back layer silica sol at a powder-liquid mass ratio of 1.5 - 2.0:1. The back layer 2 sand is manually sprinkled with mullite sand of 16 - 30 mesh and dried in a constant temperature and humidity workshop for 12 - 24 hours;

[0030] The back layer 3 includes back layer 3 slurry and back layer 3 sand. The back layer 3 slurry is prepared from mullite powder and back layer silica sol at a powder-liquid mass ratio of 2.0 - 2.2:1. The back layer 3 sand is manually sprinkled with mullite sand of 16 - 30 mesh and dried in a constant temperature and humidity workshop for 12 - 24 hours;

[0031] The back multi-layers include back multi-layers slurry and back multi-layers sand. The back multi-layers slurry is prepared from mullite powder and back layer silica sol at a powder-liquid mass ratio of 2.0 - 2.2:1. The back multi-layers sand is manually sprinkled with mullite sand of 16 - 30 mesh and dried in a constant temperature and humidity workshop for 12 - 24 hours.

[0032] This setting makes the bonding between the mold shell layers tight, not easily delaminated, and fully dried, reducing the risks such as air pocket bulging, slag falling, or water leakage during pouring.

[0033] Preferably, 5 - 9 layers are prepared for the back multi-layers.

[0034] Further, the environment during the preparation of the back layer is a constant temperature and humidity room with a temperature of 23 - 27°C and a humidity of 45 - 65%.

[0035] Compared with the prior art, the method for preparing a high surface quality titanium alloy investment casting mold shell of the present invention has the following advantages:

[0036] 1) The wax mold cleaning and drying method of the present invention increases the coating property of the surface layer slurry and improves the quality of the wax mold and the surface mold shell;

[0037] 2) The surface layer slurry preparation process of the present invention can increase the bonding strength of the surface layer, improve the shell stripping performance, and reduce the surface roughness of the casting;

[0038] 3) The vacuum impregnation process of the present invention effectively promotes the filling of the surface layer slurry into the fine patterns of the wax mold, eliminates defects such as air entrapment, air / bean bubbles in narrow slots, corners, blind holes, etc., and avoids defects such as casting tumors and slag inclusion in the subsequent casting of the casting;

[0039] 4) The back multi-layers preparation process of the present invention makes the bonding between the mold shell layers tight, not easily delaminated, and fully dried, reducing the risks such as air pocket bulging, slag falling, or water leakage during pouring. Specific Embodiments

[0040] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is given.

[0041] Example 1

[0042] A method for preparing a precision investment casting shell of a titanium alloy with high surface quality, comprising the following steps:

[0043] S1. Wax pattern cleaning

[0044] After the wax pattern is repaired, scraped, and dusted, a qualified wax pattern is obtained. The qualified wax pattern is immersed in a cleaning agent solution for washing. The cleaning agent solution is dishwashing liquid, JFC wetting agent, and water. Among them, the mass ratio of dishwashing liquid to water is 0.2%, and the JFC wetting agent accounts for 0.1% of the mass of water. After removing a large amount of wax chips and oil stains by cleaning, it is immersed in the cleaning solution for 3 times. The cleaning solution is JFC wetting agent and water. Among them, the mass ratio of JFC wetting agent to water is 0.1%. The washed wax pattern is dried. Drying environment: humidity 65% - 75%, temperature 23 - 27 °C. The dried wax pattern is immersed in the above cleaning agent solution for secondary washing and immersed in the above cleaning solution for secondary cleaning.

[0045] S2. Preparation of surface layer slurry

[0046] Specifically, the surface layer slurry uses modified silica sol. The modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator; the acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9.

[0047] Specifically, the mass fraction of SiO2 in the diluted silica sol is 17%. The specific preparation steps of the diluted silica sol are as follows: using ordinary silica sol, deionized water as the solvent, diluting the silica dioxide content to 17%, adding a pH value regulator to adjust the pH value to 9, and stirring for about 36 h. Among them, the pH value regulator is NaOH solution and HCl solution.

[0048] Specifically, the mass ratio of the diluted silica sol to the PVA solution is 20:1. The mass fraction of PVA in the PVA solution is 15%. The PVA solution is PVA and solvent water. Yttrium oxide powder with a mesh size of 325 is added to the modified silica sol at a powder-liquid mass ratio of 4:1, and a JFC wetting agent is added. Among them, the JFC wetting agent accounts for 0.03% of the total mass of the modified silica sol and yttrium oxide powder. The mechanical stirring speed is 200 r / min for dispersion, and a surface layer slurry with a flow cup viscosity of 8 s is prepared at room temperature.

[0049] S3. Preparation of surface layer

[0050] Place the wax pattern into a container, pour the above-mentioned surface layer slurry into the container, and submerge the wax pattern to a certain height, with the height being sufficient to cover the wax pattern. Place the entire container into a vacuum equipment, seal it properly, set a certain vacuum degree and start the vacuum equipment. The vacuum degree is -0.09 MPa. After the wax pattern stops bubbling, end the vacuum treatment, manually release the negative pressure, and the liquid level of the surface layer slurry drops, completing the vacuum dipping of the wax pattern; then apply the surface layer to other parts of the wax pattern that have not been dipped, and the traditional application method can be used. Then sprinkle sand in the rain-like sand-sprinkling method, and the sand material for the surface layer sand is yttrium oxide sand, with a mesh number of 60 - 120 meshes. The surface layer drying is carried out in a constant temperature and humidity workshop, with a drying time of 10 hours, a temperature of 24 °C, and the humidity not being lower than 75%.

[0051] For the shell molds with complex and delicate structures such as narrow slits, narrow grooves, micropores, or high surface precision requirements, the surface layer vacuum dipping can be repeated 2 times after drying.

[0052] S4. Back layer preparation

[0053] The back layer slurry is composed of back layer silica sol and mullite powder, and the back layer sand uses mullite sand.

[0054] The said back layer silica sol is silica sol with a SiO2 content of 30%, the mullite powder uses 200-mesh mullite powder, and the back layer sand uses 16 - 60-mesh mullite sand.

[0055] For the first back layer, prepare the first back layer slurry with the above-mentioned silica sol and mullite powder according to the powder-liquid mass ratio of 1.2:1, and use manual sand-sprinkling with 30 - 60-mesh mullite sand for the first back layer sand, and dry it in a constant temperature and humidity workshop for 12 hours;

[0056] For the second back layer, prepare the second back layer slurry with the above-mentioned silica sol and mullite powder according to the powder-liquid mass ratio of 1.7:1, and use manual sand-sprinkling with 16 - 30-mesh mullite sand for the second back layer sand, and dry it in a constant temperature and humidity workshop for 12 hours;

[0057] For the third back layer, prepare the third back layer slurry with the above-mentioned silica sol and mullite powder according to the powder-liquid mass ratio of 2.1:1, and use manual sand-sprinkling with 16 - 30-mesh mullite sand for the third back layer sand; dry it in a constant temperature and humidity workshop for 12 hours;

[0058] For the third to fifth back layers, prepare the third to fifth back layer slurries with the above-mentioned silica sol and mullite powder according to the powder-liquid mass ratio of 2.1:1, and use manual sand-sprinkling with 16 - 30-mesh mullite sand for the third to fifth back layer sands; dry it in a constant temperature and humidity workshop for 12 hours;

[0059] The temperature in the back layer constant temperature and humidity room is 23 - 27 °C, and the humidity is 45 - 65%.

[0060] After the above-mentioned back layer is prepared, a mold shell is obtained through dewaxing, baking, pouring, and shell cleaning. Among them, dewaxing, baking, pouring, and shell cleaning all adopt conventional existing processes, which will not be described in detail here. Using the above mold shell for precision casting to produce complex precision castings with a wall thickness of 0.7 mm, the slender narrow slits and micropores are formed completely, and there are no casting defects such as titanium beads and slag inclusions.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that the qualified wax pattern is only cleaned in the cleaning solution, and the prepared mold shell is used for precision casting to produce complex precision castings with a wall thickness of 0.7 mm.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that the surface layer prepared with the publication number CN102284678A is used, and the prepared mold shell is used for precision casting to produce complex precision castings with a wall thickness of 0.7 mm.

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is that the traditional process is as follows: wax pattern making, wax pattern trimming, wax pattern assembly welding. When making the surface layer, the surface layer binder uses ordinary silica sol, the surface layer powder uses 325-mesh yttrium oxide powder, the surface layer sand uses 60-80-mesh yttrium oxide sand, and the coating is carried out by manual slurry pouring or dipping without vacuum negative pressure dipping technology; when strengthening the back layer, the coating and sand spreading process is repeated, and there is no coordinated matching of the mass ratio of the back layer powder and liquid, the back layer sand, and the environmental conditions. The prepared mold shell is used for precision casting to produce complex precision castings with a wall thickness of 0.7 mm.

[0067] Performance Test

[0068] The surface roughness, filling integrity, titanium beads, surface slag, first-pass yield, and surface contamination layer thickness of the complex precision castings in Example 1 and Comparative Examples 1-3 are tested. Among them, 288 castings are produced in batch, and by detecting the filling integrity, surface slag, titanium beads, and first-pass yield of each casting, the filling integrity / % = the number of completely filled parts n / 288, the surface slag / % = the number of parts with surface slag m / 288. Similarly, the titanium beads / % = the number of parts with titanium beads x / 288, the first-pass yield / % = 100% - the surface slag / %. The surface roughness and surface contamination layer thickness both refer to the average corresponding indicators; the test results are shown in Table 1.

[0069] Table 1 Test Results of Related Performance of Castings in Example 1 and Comparative Examples 1-3

[0070]

[0071] It can be seen from Example 1 and Comparative Example 1 in Table 1 that the wax mold of the present invention is cleaned with a cleaning agent solution and a cleaning solution, which can increase the coatability of the surface layer slurry, improve the quality of the surface shell mold, and for the precision casting obtained after casting the shell mold, its filling integrity and the qualified rate of one-time forming are correspondingly improved, and the surface roughness, titanium beads, surface slag, and thickness of the surface pollution layer all reach a relatively low level.

[0072] It can be seen from Example 1 and Comparative Example 2 in Table 1 that by subjecting the surface layer slurry of the present invention to vacuum treatment, the quality of the surface shell mold is improved, and for the precision casting obtained after casting the shell mold, its filling integrity and the qualified rate of one-time forming are correspondingly improved, and the surface roughness, titanium beads, surface slag, and thickness of the surface pollution layer all reach a relatively low level.

[0073] It can be seen from Example 1 and Comparative Example 3 in Table 1 that the traditional process not only has low filling integrity and the qualified rate of one-time forming, but also has a high surface roughness and is not suitable for making precision castings. The shell mold obtained by the present invention compared with the traditional process can be used for casting precision castings, and the surface defects of the castings are less.

[0074] In summary, in the preparation method of the shell mold of the present invention, through the coordinated interaction of multiple steps such as the cleaning, drying, preparation of the surface layer slurry, preparation of the surface layer, and preparation of the backing layer of the wax mold and the corresponding process parameters, compared with the shell mold prepared by the traditional method, the surface finish of the shell mold, the integrity of the replication of the detailed shape, and the high qualified rate of one-time forming are all significantly improved.

[0075] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for preparing a high-surface-quality investment casting shell of titanium alloy, characterized in that, It includes the following steps: S1. Wax pattern cleaning: The wax pattern is successively cleaned with a cleaning agent solution and a cleaning solution, and steps 1 to 3 are repeated 1 to 3 times; S2. Preparation of surface layer slurry; S3. Preparation of surface layer; S4. Preparation of back layer.

2. The preparation method according to claim 1, wherein In step S1, the cleaning agent solution includes dishwashing liquid, JFC wetting agent, and clear water. Among them, the mass fraction of dishwashing liquid is 0.1% to 0.3%, and the mass fraction of JFC wetting agent is 0.03% to 0.15%.

3. The preparation method according to claim 1, characterized in that In step S1, the cleaning solution includes JFC wetting agent and clear water, and the mass fraction of JFC wetting agent is 0.03% to 0.15%.

4. The preparation method according to claim 1, characterized in that, In step S2, the surface layer slurry uses modified silica sol. The modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator. The mass ratio of the diluted silica sol to the PVA solution is 15 to 25:

1. The mass fraction of PVA in the PVA solution is 10% to 20%. The acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9 to 10.

5. The preparation method according to claim 4, characterized in that, The mass fraction of SiO2 in the diluted silica sol is 15% to 20%.

6. The preparation method according to claim 4, characterized in that, In step S2, the specific steps are as follows: Add yttrium oxide powder to the modified silica sol, where the powder-liquid mass ratio is 3.5 to 5.5:1, and then add JFC wetting agent and disperse evenly to prepare a surface layer slurry with a flow cup viscosity of 6 to 12 s.

7. The preparation method according to claim 6, characterized in that, The mesh number of the yttrium oxide powder is 200 to 400 mesh.

8. The preparation method according to claim 1, characterized in that, In step S4, when preparing the back layer, back layer slurry and back layer sand are used. The back layer slurry includes back layer silica sol and mullite powder. The back layer silica sol is silica sol with a SiO2 content of 30%. The mullite powder uses 200-mesh mullite powder, and the back layer sand uses 16 to 60-mesh mullite sand.

9. The preparation method according to claim 1, characterized in that, In step S4, the back layer includes back layer 1, back layer 2, back layer 3, and multiple back layers. Multiple back layers refer to more than three layers.

10. The preparation method according to claim 9, characterized in that, The specific back layer is as follows: Back layer 1 includes back layer 1 slurry and back layer 1 sand. The back layer 1 slurry is prepared by mixing mullite powder and back layer silica sol according to a powder-liquid mass ratio of 1.0 to 1.5:

1. The back layer 1 sand uses manually sprinkled 30 to 60-mesh mullite sand and is dried in a constant temperature and humidity workshop for 12 to 24 hours; Back layer 2 includes back layer 2 slurry and back layer 2 sand. The back layer 2 slurry is prepared by mixing mullite powder and back layer silica sol according to a powder-liquid mass ratio of 1.5 to 2.0:

1. The back layer 2 sand uses manually sprinkled 16 to 30-mesh mullite sand and is dried in a constant temperature and humidity workshop for 12 to 24 hours; Back layer 3 includes back layer 3 slurry and back layer 3 sand. The back layer 3 slurry is prepared by mixing mullite powder and back layer silica sol according to a powder-liquid mass ratio of 2.0 to 2.2:

1. The back layer 3 sand uses manually sprinkled 16 to 30-mesh mullite sand and is dried in a constant temperature and humidity workshop for 12 to 24 hours; Multiple back layers include multiple back layer slurries and multiple back layer sands. The multiple back layer slurries are prepared by mixing mullite powder and back layer silica sol according to a powder-liquid mass ratio of 2.0 to 2.2:

1. The multiple back layer sands use manually sprinkled 16 to 30-mesh mullite sand and are dried in a constant temperature and humidity workshop for 12 to 24 hours.

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